Polyphase stirring of molten metal



Nov. 11, 1969 R. s. SEGSWORTH 3,473,156

POLYPHASE STIRRING OF MOLTEN METAL Filed Feb. 15, 1968 2 Sheets-Sheet 1 ATTORNEY Nov. 11, 1969 5, SEGSWORTH 3,478,156

POLYPHASE STIRRING OF MOLTEN METAL Filed Feb. 15, 1968 2 Sheets-Sheet 2 STIRRING Fig/4a Roberz 6/0 65/ MELTING /N VE N TOR 5 6 war #7 3,478,156 POLYPHASE STIRRING OF MOLTEN METAL Robert Sidney Segsworth, Toronto, Ontario, Canada, as-

signor to Ajax Magnethermic Corporation, Warren, Ohio, a corporation of Ohio Filed Feb. 15, 1968, Ser. No. 705,848 Int. Cl. H05b 5/12, 5/00, 9/06 U.S. CI. 1327 9 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a method and apparatus for polyphase stirring and/or melting from a single phase source of alternating current.

An object of this invention is to achieve increased stirring in a coreless melting or holding furnace.

A further object of this invention is to provide polyphase stirring in a coreless melting or holding furnace with a single phase source.

A still further object of this invention is to provide said polyphase stirring but eliminating violent agitation of the melt surface.

Another object of this invention is to provide polyphase stirring of molten metal with improved electrical efiiciency.

A further object of this invention is to provide a coreless melting or holding furnace wherein transfer from single phase melting to polyphase stirring is accomplished in a relatively simple, economical and expeditious manner.

Another object of this invention is to provide for transfer from polyphase stirring in a coreless melting or holding furnace to single phase melting.

A still further object of this invention is to provide stirring means for a coreless melting or holding furnace wherein the direction of stirring may be readily reversed. A still further object is to provide polyphase stirring of molten metal in pipe lines to move or pump the same.

Other objects of the invention and the invention itself will become more readily apparent by reference to the accompanying drawings, in which:

FIGURE 1 is a longitudinal vertical sectional view of a furnace embodying the invention including electrical circuit connections;

FIGURE 1A is a view showing a phase vector diagram of the coil currents of FIGURE 1;

FIGURE 2 is a View similar to FIGURE 1 showing a switching connection between the two coil sections of FIGURE 1;

FIGURE 2A is a phase vector diagram identical with that of FIGURE 1A showing in dotted lines the phase angle of the current 1B when the switch of FIGURE 2 is closed;

FIGURE 3 is a view similar to FIGURE 1, but showing a modification of the invention wherein four coil sections are used;

FIGURE 3A is a phase vector diagram of the coil curcents of FIGURE 3;

FIGURE 4 is a view similar to FIGURE 1 of another United States Patent 0 Patented Nov. 11, 1969 modification of the invention disclosing switches for reversing the direction of flow of the metal in a furnace;

FIGURE 4A is a phase vector diagram of the coil curcerzlts of FIGURE 4 during polyphase upward stirring; an

FIGURE 4B is a phase vector diagram of the coil currents of FIGURE 4 during melting.

Referring now more particularly to the drawings, in all of which like parts are designated by like reference characters, a coreless melting or holding furnace 10 and, as shown, with a crucible having a refractory lining 10', surrounded by a coil of two or more sections. Sections of said coil are connected to a single phase alternating current power source and other of said sections are unconnected thereto. The said alternating current is applied so that the phase preferably shifts by the same angle from one coil section to the next, as shown in the current vector FIGURES 11:, 2a, 3a and 4a, wherefor positive unidirectional motion of the outer portion of the melt in the direction in which the travelling magnetic field moves is achieved. Thus, it is possible to obtain either upward or downward movement (see FIG. 4) in the outer portion of the normally cylindrical melt while a unidirectional return flow in the opposite direction generally prevails in the center portion.

In the embodiment of FIGURE 1, a pair of coaxial spaced coils A and B surround the furnace. The bottom coil A is shown supplied with alternating current from a single phase generator, frequency multiplier, or other a1- ternating current source 11. A bank of capacitors 12, 12' connected in parallel in the input line are adapted to be added or subtracted by switching means 13 to improve the power factor.

The coaxial coil section or upper section B is connected to a bank of capacitors 14, 14, similar to those designated at 12, 12, and said capacitors 14, 14' are adapted to be switched in and out as required by switch means 15. The coil section B is not connected to the power source.

It has been found that in this arrangement the amount of capacitors connected to the upper section may be adjusted to produce resonance or near resonance in tune with the circuit of coil section A with the result that a very substantial upward stirring of the melt at the sides of the crucible 10 results with corresponding downward flow in the center section of the melt as shown in FIGURE 1. Under these circumstances the phase angle of the current 1 through the upper section B lags the current in the lower section 1 by approximately as shown in the current vector diagram FIGURE 1a.

The phase angle shown in FIGURE la, it will be understood, can be adjusted within a wide range from substantially less than 90 to substantially more than 90 without significantly affecting the current itself or the upward stirring effect produced. It is generally found desirable to tune the upper coil close to resonance.

Coreless furnace installations of the prior art provide at least two separate sources of voltage with a substantial phase angle between them to accomplish polyphase stirring and are usually designed to operate at maximum power for melting from a single-phase high power supply and at a reduced power level for polyphase stirring by transferring each coil section from such single phase high power supply to one phase of a polyphase supply, since it is normally not desirable to melt in the polyphase mode since a significant loss of electrical efliciency would take place and a strong agitation of the melt surface which could be deleterious and detrimetal to the metallurgy. A

large number of switches and at least partial duplication of voltage regulating facilities is required therefor, hence the transfer is costly and complicated in such installations.

In FIGURE 2, an arrangement for transferring the system of FIGURE 1 from melting to stirring is illustrated. It will be noted that a fixed electrical connection 16 between the bottom terminals of the two coil sections B and A and a tie-line 18 with a single switch means 17 between the upper terminals of coil sections B and A has been added to the showing of FIGURE 1. Conversion from stirring to melting is accomplished, in this form of the invention, by closing the switch 17 as indicated by dotted lines so that both sections B and A now operate as parallel sections of a single-phase coil in a conventional manner. The capacitors 12, 12, 14, 14 can then be readjusted manually or automatically, act jointly and are fully utilized to correct the power factor of the single phase furnace.

It is proposed that taps may be provided on the induction coil or a transformer interposed between the induction coil and the capacitors, or a transformer interposed between said coil and the capacitors and that in such event the tap or transformer setting may be adjusted when transferring from stirring to melting operation. It is believed that such tap or transformer setting adjustments are of the type readily understood by those skilled in the art to which the present invention appertains.

The effectiveness of polyphase stirring, it has been found, generally improves with the number of separately phased coil sections used, hence, in the form of the invention shown in FIGURE 3, the furnace is disclosed with four sections designated as A, B, C and D in sequence from the bottom coil upward to the top coil section.

If upward stirring is desired as shown by arrows in the form of FIGURE 3, the generator or other single-phase power source is connected to coils A and C and this connection may be in series or in parallel. However, such coils must be connected in a way, as shown, that their electro-magnetic fields buck or oppose each other. In other words, I and I as shown in FIGURE 3, are substantially 180 out of phase.

A battery of capacitors, as shown, with fixed and variable capacity, is connected, in the form of FIGURE 3, to sections B and D in series, but again in such a manner that the current in these two sections will magnetically buck each other or be 180 out of phase with each other.

It will be apparent that parallel bucking may be used in this form of the invention, but the series connection which is shown in FIGURE 3 is preferably used for the enenergized B and D sections. As shown, if the battery of capacitors 14, 14' is tuned to resonance or near resonance, the current 1 lags the current I by approximately 90; the current 'I as hereinbefore described is 180 out of phase with the current I and, hence, lags the current I by 90. Finally, the current I lags I by 180 and, therefore, lags the current in section C by approximately 90". The four currents referred to hereinabove, viz. I 1 I and I are illustrated in FIGURE 3a by vectors opposite the separate coil sections illustrated in FIGURE 3. The current in each section, it will be noted, lags behind that in the section below it by approximately 90. The resulting full wave travelling field produces upward fiow as shown by arrows in FIG- URE 3 in the outer layers of the melt in an improved manner over that of FIGURE 1.

It has sometimes been found desirable to provide a furnace that can be provided with upward stirring or downward stirring at the operators option and a furnace that can melt in a normal single-phase operation and in addition be capable of stirring either upwardly or downwardly at the operators option.

In FIGURE 4, a switching arrangement -is disclosed wherefore transfer may be made from polyphase stirring to single-phase melting with the basic four phase stirring connection shown in FIGURE 3. A switch 30 is provided to connect sections B and D to the generator or other single phase source so that all four sections A, B, C and D, respectively, may be placed in phase for melting rather than 180 apart, as required in stirring. The circuit of FIGURE 4 provides that in the melting operation, sections A and C and B and D are connected in series and both groups then connection in parallel to the single phase source or generator. Each section then operates at approximately /2 the generator voltage and all four sections, A, B, C and D contribute approximately the same power.

It will be obvious that coil taps or transformers, as previously described in connection with FIGURE 2, may be employed in the form of the invention as shown in FIGURE 4.

FIGURE 4b is a vector diagram of the currents of sections A, B, C and D during the melting operation and FIGURE 4a is a vector diagram of the currents I I I and I during the stirring operation and in said operation the current in each section, similarly to that shown in FIGURE 3a, lags behind that in the section below it by approximately and also produces a full-wave upward travelling field producing upward flow in the outer layers of the melt.

To reverse the stirring action shown in solid line arrows in FIGURE 4, the power source may be connected to the upper sections D and B and capacitance only to the lower sections C and A so that the current in the lower section will lag the upper section and thus producing downward flow, as indicated in dotted line arrows, in the outer portion of the melt and upward flow in the center of the melt. This may be effected, for example, by closing switch 30 and opening switch 40 shown in dotted lines.

The polarity of coil sections C and D is reversed as by switch means 21, 32 so that the currents in sections A and C, and in B and D, respectively, will be in phase for melting rather than apart, as required for stirring. The switch 30, shown in FIGURE 4, is similar to the switch 17 in FIGURE 2, employed to provide a tieline connection to the upper sections, wherefore sections A, B, C and D are all energized from the same singlephase power source and maximum power is obtained for melting.

Although the invention has been described in connection with coreless melting or holding furnaces, it will be obvious that the same may be employed for moving or pumping molten metal in pipe lines by creating a travelling electro-magnetic field and in such application, since the liquid is free to travel, it should be noted that the flow will be unidirectional throughout the body of molten irinetal, the center being carried along by the peripheral It will further be obvious that an increased number of sections for example, either or more coil sections may be used in the furnaces and that the effectiveness of the polyphase stirring will increase as the frequency is lowered and improves with the number of separately phased coil sections used.

Further, it will be understood that the invention may be opearted at the normal line frequency of 60 cycles, or preferably at other frequencies such as a 180 cycle, 960 cycle, 30 cycles, etc. Such frequencies are normally available in single-phase form, whereas, three-phase supply is generally available from 60 cycle.

Although I have described my invention in connection with certain preferred embodiments, I am aware that numerous and extensive departures may be made therefrom without, however, departing from the spirit of my invention or the scope of the appended claims.

What I claim is:

1. In combination, a plural-section coil, a molten metal container, said plural-section coil comprising separate coil sections surrounding different portions of said container, a single phase power supply, said coil sections being coaxial and axially adjacent each other, a first of said sections being connected and energized by said power supply, a second of said sections being connected to capacitance and unconnected to said power supply, the current in said second unconnected section being substantially displaced in phase from the current in such first section thereby producing polyphase unidirectional stirring movement in the molten metal.

2. A coil as claimed in claim 1 wherein said second of said sections is tuned substantially to the frequency of said power supply.

3. In the combination of claim 1, means for adjusting said capacitance to substantially achieve resonance at the frequency of said single phase power supply.

4. In the combination of claim 1, said separate sections having currents of difierent phase applied to the same during stirring and means whereby currents of the same phase may be applied to all of the said sections for melting.

5. In the combination of claim 1, a lower section being connected to said single phase power supply and an upper section being connected to said capacitance but unconnected to said power supply producing polyphase stirring, said sections having currents of different phase applied to the same during stirring and means whereby currents of the said phase may be applied to the said sections for melting.

6. In the combination of claim 1, means for adjustment of the phase angle between the coil sections.

7. In the combination of claim 1, means for transferring from polyphase stirring of the molten metal in the furnace to single phase melting.

8. In the combination of claim 1, means for reversing the connections of said sections whereby said one section connected to said supply is disconnected therefrom being connected solely to said capacitance and said other section is connected to said supply.

9. In combination, a four-section coil, a molten metal container, said four-section coil comprising four separate coil sections surrounding different portions of said container, a single phase power supply, said coil sections being coaxial and axially adjacent each other, a first of said sections being connected and energized by said power supply, a second of said sections being serially connected to capacitance and unconnected to said power supply, a third of said sections being connected and energized by said power supply, a fourth of said sections being serially connected to capacitance and unconnected to said power supply, the phase angle of current in each of said sections lagging that of the current in the preceding section by substantially thereby producing polyphase unidirectional stirring movement in the molten metal.

References Cited UNITED STATES PATENTS 1,822,539 9/1931 Northrup 132.7 2,052,649 9/ 1936 Patterson 219-l0.75 2,803,689 8/1957 Hnilicka 219-1035 FOREIGN PATENTS 668,5 42 8/1963 Canada.

JOSEPH V. TRUHE, Primary Examiner L. H. BENDER, Assistant Examiner US. 01. x13, 2 9 10.75

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,478,156 November 11, 1969 Robert Sidney Segsworth It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

"energized" should read unenergized Column 3, line 47,

insert upward Column 4, line 33,

line 59, after "full wave" "21" should read 31 Signed and sealed this 10th day of November 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr. Attesting Officer 

